Use of organic amides as anti-coagulants in emulsions prepared by the gelatin derivative coagulation wash procedure



United States Patent M ABSTRACT OF THE DISCLOSURE Silver halide emulsions Containing gelatin derivatives and a small amount of an organic amide as a coagulation suppressor.

This invention relates to the prevention of coagulation in photographic emulsions containing gelatin derivatives by incorporating a small amount of an organic amide in the emulsion.

The preparaiton of washed silver halide photographic emulsions by the use of gelatin derivatives has been described in the prior art such as for example in U.S. Patents Nos. 2,614,928, 2,614,929, and 2,614,931. This procedure involves the preparation of silver halide grains in a gelatin derivative peptizer, and the grains held by the gelatin derivative are separated from water soluble salts by a coagulation wash procedure. After the removal of the water soluble salts the silver halide grains are redispersed in a vehicle for the silver halide which may be gelatin or some polymeric or synthetic resin vehicle.

It is frequently advantageous to add divalent salts such as salts of lead, zinc, manganese, cadmium, etc. to photographic emulsions to impart various characteristics thereto; for instance, the addition of divalent salts such as cadmium chloride, to photographic emulsions is described in U.S. Patent No. 2,839,405 and Glafkides Photographic Chemistry, vol. I, p. 318. The addition of divalent salts to silver halide emulsions which contain gelatin derivatives has been found to cause a certain amount of coagulation or formation of insoluble particles. Thus this affects uniform coating operations and is usually undesirable in the making of photographic products.

It is often advantageous to coat out photographic emulsions while under acid conditions such as at a pH of 34. Sometimes at a lowered pH of this type silver halide emulsions containing gelatin derivatives may settle and contribute to nonuniformity in the coating operations. When both divalent salts are present and the composition employed in coating has a low pH the effect obtained is particularly undesirable.

One object of my invention is to provide silver halide photographic emulsions having a gelatin derivative content therein which exhibits uniformity in coating even though divalent salt has been added or a low pH is used. Another object of my invention is to provide washed silver halide photographic emulsions containing an organic amide. Other objects of my invention will appear herein.

I have found that if a silver halide photographic emulsion, in whose preparation a gelatin derivative acid coagulation wash procedure was used, contains an organic amide such as dimethyl formamide or the like, that divalent salt antifoggants may be added to this emulsion or the pH thereof may be appreciably lowered and the emulsion thus treated will show no coagulation or formation of settled particles therein. As a consequence when such emulsions are coated out onto a support such as film base or paper base coatings of good uniformity are obtained.

My invention is applicable to various silver halide 3,359,110 Patented Dec. 19, 1967 emulsions whether the silver halide is silver chloride, silver bromoiodide, or some other type of silver halide grain, the grains having been prepared and washed by a gelatin derivative acid coagulation Wash procedure. This may involve either the preparation of the silver halide grains initially in the gelatin derivative as the peptizer for the silver halide or the grains may have been prepared in some other peptizer such as gelatin and the gelatin derivative was mixed therewith prior to the acid coagulation by which the grains were separated from the liquid portion of the silver halide dispersion.

I have found that the effective proportion of organic amide varies over wide limits but that usually an amount within the range of 1-100 parts of amide per parts of gelatin in the photographic emulsion is suitable. I have found that proportions within the range of 1075 parts of organic amide per 75 parts of gelatin are especially effective.

In the making of the photographic emulsion the silver halide dispersion is first prepared, dispersed in a gelatin derivative such as an acid anhydride or acid chloride derivative of gelatin. Upon lowering the pH, such as by adding dilute sulfuric acid to bring the pH down to 3-3.5, especially under cool conditions, a coagulum is formed which is separated from the aqueous liquid containing the water soluble salts. If desired, the coagulum may be then washed in cold water. The photographic emulsion is formed by redispersing the coagulum in an aqueous solution of a vehicle, at a suitable pH, which vehicle may be gelatin, 2. gelatin derivative, a synthetic resin vehicle such as polyvinyl alcohol or for hydrolyzed cellulose ester. In accordance with my invention organic amide is then added to the emulsion which amide inhibits any coagulation effect which might be experienced in further treatments of the emulsion especially as might result by the addition of cadmium chloride or such other divalent salt or in lowering the pH of the emulsion for some purpose.

The following non-limiting examples are provided to illustrate the invention.

Example 1 A silver halide emulsion was prepared following the procedure described in Example 5 of U.S. Patent No. 2,614,928. The total gelatin present was 75 grams per mole of silver halide and the weight of the emulsion was divided into equal parts. To one part of the emulsion, 15 cc. of dimethyl formamide was added. There was then added to each portion 2 /2 grams of cadmium chloride. The portion to which the dimethyl formamide had been added was stable upon standing whereas that to which the cadmium chloride had been added without the previous addition of dimethyl formamide appeared grainy and non-uniform in nature.

Example 2 An emulsion was prepared in the same manner as in the preceding example except that the alkali metal salt used in preparing the silver halide was a mixture of sodium chloride and potassium bromide in a 65:33 chloro-. bromide ratio instead of potassium bromide and potassium iodide. The washed silver halide emulsion thus prepared was divided into equal parts. To one part was added 15 cc. of dimethyl formamide while to the other portion no addition was made prior to lowering the pH to 4 which was done with both portions of the emulsion. The emulsion to which the dimethyl formamide had been added was found to be stable and upon standing retained its normal appearance. That which had been acidified without the previous addition of dimethyl formamide showed grain and non-uniformity after a short time of standing.

3 Example 3 A fine grain silver chlorobromide emulsion was prepared as described in the preceding example but using a ratio of 80 mole percent chloride and 20 mole percent bromide and the gelatin derivative used as the peptizer was a maleic anhydride derivative of gelatin as described in Example 6 of U.S. Patent No. 2,614,928. The emulsion was divided into several portions each of which contained .05 mole of silver halide, and about 2 grams of the gelatin derivative. Various amides were added to the various portions except for number 1 in the amounts shown in the appended table. Each portion was poured into a separate 50 ml. graduated cylinder and 1 ml. of a 1.84 M cadmium chloride solution was added to each portion. The various graduated cylinders were placed in a constant temperature bath at 41 C. and held for three hours. The table indicates the results in each case.

Amide Amount Results (1) None Coagulation. (2) Dimethyl i'ormamide 1 No coagulation. (3) Dimethyl iormamida. 0.5 Do. t) Dimetliyl acetamide... 0.5 Do. (5) N-Q-hydroxy ethyl formamide 0.5 Do. (6) Hexamethyl phosphoric triamide 0.5 Do. (7) N-methyl pyrrolidone 0.5 Do.

Example 4 A photographic emulsion was prepared as described in Example 1 except that the gelatin derivative employed was a m-carboxy benzene sulfonyl derivative of gelatin. The emulsion was put through the same procedure as described in the preceding example and the following re- An additional advantage for the use of organic amide in acid coagulated gelatin derivative washed emulsions resides in the stabilizing of those emulsions against coagulation when those emulsions are mixed with acid resins such as alkyl acrylate-acrylic acid copolymers, e.g. a butyl acrylate-acrylic acid copolymer. Examples of acid polymeric latices as well as water-soluble acid polymer solutions which tend to coagulate silver halide emulsions containing gelatin derivatives are cellulose ether esters of the type described in U.S. Patent No. 2,725,293; acrylateacrylic acid copolymers of the type described in U.S. Patent No. 3,062,674; carboxylated polyvinyl acetals of the type described in U.S. Patent No. 3,003,879; dibasic acid esters of polyvinyl alcohol as described in U.S. Patent No. 3,000,741. Unless photographic emulsions of this type have been stabilized in some way the addition of polymeric material of this type tends to cause settling after standing of the emulsion for a short time. Hence, difiiculties are often met with in coating operations using photographic emulsions in which certain acid type polymers have been employed. It has been found that the addition to an emulsion, to which a small amount of organic amide has been added, of the copolymer inhibits coagulation or particle formation and a good coating is easily obtained therewith. Conveniently, the addition of about 2 ounces of dimethyl formamide to approximately 3 pounds of the photographic emulsion before adding the copolymer is very satisfactory.

The invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, but'it will be understood that variations and modifications can be elfected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

I claim:

1. A silver halide photographic emulsion having a pH below 7 containing an acid coagulable gelatin derivative selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anhydride derivatives of gelatin, the aromatic isocyanate derivatives of gelatin and the 1,4 diketone derivatives of gelatin and an organic amide which suppresses coagulation of the gelatin derivative, said organic amide being selected from the group consisting of N-Z-hydroxyethyl formamide, hexamethyl phosphoric triamide, N-(lower alkyl)pyrrolidone and amides having the formula R1 RGN/ ll 0 R2 wherein R, R and R each represents a lower alkyl group.

2. A silver halide photographic emulsion having a pH below 7 containing a phthalic anhydride derivative of gelatin and an organic amide which suppresses coagulation of the gelatin derivative, said organic amide being selected from the group consisting of N-2-hydroxyethyl formamide, hexamethyl phosphoric triamide, N-(lower alkyl)pyrrolidone and amides having the formula ll o wherein R, R and R each represents a lower alkyl group.

3. A silver halide photographic emulsion having a pH below 7 containing a maleic anhydride derivative of gelatin and an organic amide which suppresses coagulation of the gelatin derivative, said organic amide being selected from the group consisting of N-2-hydroxyethyl formamide, hexamethyl phosphoric triamide, N-(lower alkyl)- pyrrolidone and amides having the formula RCN wherein R, R and R each represents a lower alkyl group.

4. A silver halide photographic emulsion in accordance with claim 1 wherein the organic amide is dimethyl formamide.

5. A silver halide photographic emulsion in accordance with claim 1 wherein the organic amide is N-methyl pyrrolidone.

6. A silver halide photographic emulsion in accordance with claim 1 wherein the organic amide is dimethyl acetamide.

7. A silver halide photographic emulsion having a pH below 7 containing a phthalic anhydride derivative of gelatin and dimethyl formamide to suppress coagulation of the gelatin derivative.

8. A silver halide photographic emulsion having a pH below 7 containing a maleic anhydride derivative of gelatin and dimethyl formamide to suppress coagulation of the gelatin derivative.

9. A silver halide photographic emulsion having a pH below 7 containing an acid coagulable gelatin derivative selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anhydride derivatives of gelatin, the aromatic isocyanate derivatives of gelatin and the 1,4 diketone derivatives of gelatin, an alkyl acrylate-acrylic acid copolymer and an organic amide which suppresses coagulation of the gelatin derivative, said organic amide being selected from the group consisting of N-Z-hydroxyethyl formamide, hexamethyl phosphoric triamide, N-(lower alkyl)pyrrolidone and amides having the formula RON wherein R, R and R each represents a lower alkyl group.

10. A silver halide photographic emulsion having a pH below 7 containing a phthalic anhydride derivative of gelatin, an alkyl acrylate-acrylic acid copolymer and dimethyl formamide to suppress coagulation of the gelatin derivative.

11. A silver halide photographic emulsion in accordance with claim 1 containing a divalent salt.

12. A silver halide photographic emulsion in accordance with claim 1 containing a cadmium salt.

13. A silver halide photographic emulsion in accordance with claim 1 containing cadmium chloride.

14. A silver halide photographic emulsion in accordance with claim 7 containing a cadmium salt.

15. A silver halide photographic emulsion in accordance with claim 7 containing cadmium chloride.

16. A silver halide photographic emulsion in accordance with claim 8 containing a cadmium salt.

17. A silver halide photographic emulsion in accordance with claim 8 containing cadmium chloride.

References Cited UNITED STATES PATENTS 2,592,263 4/1952 Frame 96-94 2,614,929 10/1952 YutZy et al. 9694 2,768,079 10/1956 Russell 9694 3,062,674 11/1962 Houck et a1. 96-114 3,223,528 12/1965 Urancken et al 96-94 NORMAN G. TORCHIN, Primary Examiner.

20 I. TRAVIS BROWN, Examiner. 

1. A SILVER HALIDE PHOTOGRAPHIC EMULSION HAVING A PH BELOW 7 CONTAINING AN ACID COAGULABLE GELATIN DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF THE AROMATIC SULFONYL CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID ANHYDRIDE DERIVATIVES OF GELATIN, THE AROMATIC ISOCYANATE DERIVATIVES OF GELATIN AND THE 1,4 DIKETONE DERIVATIVES OF GELATIN AND AN ORGANIC AMIDE WHICH SUPPRESSES COAGULATION OF THE GELATIN DERIVATIVE, SAID ORGANIC AMIDE BEING SELECTED FROM THE GROUP CONSISTING OF N-2-HYDROXYETHYL FORMAMIDE, HEXAMETHYL PHOSPHORIC TRIAMIDE, N-(LOWER ALKYL) PYRROLIDONE AND AMIDES HAVING THE FORMULA 